A liquid crystal display device is one example of a display device which displays an image. The liquid crystal display device includes a liquid crystal panel serving as a spatial modulation element and a planar lighting device (a backlight) emitting light toward the back of the liquid crystal panel. The light passing through the liquid crystal panel is spatially modulated and, as a result, an image is formed on the liquid crystal panel.
Examples of the liquid crystal display device include a two-dimensional (2D) display capable of displaying two dimensions and a three-dimensional (3D) display capable of displaying three dimensions.
Firstly, a configuration of a conventional 2D display is described. FIG. 11 is a diagram showing a configuration of a conventional liquid crystal display device 20 capable of 2D displaying. The liquid crystal display device 20 shown in the diagram includes a light source 201, a light guide plate 202, a diffuser plate 203, a liquid crystal panel 204, and a control unit 205. The control unit 205 controls the light source 201 and the liquid crystal panel 204.
Light emitted from the light source 201 enters a side surface 202a of the light guide plate 202. The light entering the side surface 202a of the light guide plate 202 is transmitted through the light guide plate 202. Then, the traveling direction of the light is changed by a prism unit 202c provided at the bottom surface of the light guide plate 202. After this, the light is emitted from a main surface 202b of the light guide plate 202. The light emitted from the main surface 202b of the light guide plate 202 is diffused by the diffuser plate 203, and then illuminates the liquid crystal panel 204. Here, the light diffused by the light by the diffuser plate 203 allows the display luminance to be uniform on the liquid crystal panel 204. By illuminating the liquid crystal panel 204 with the light emitted from the light source 201 in this way, the liquid crystal display device 20 can provide 2D displaying to a user 60.
A method of configuring the aforementioned diffuser plate 203 with a liquid crystal element has been proposed (see Patent Literature 1, for example). In this case, the control unit 205 controls a voltage to be applied to the liquid crystal element of the diffuser plate 203. With this, the diffuser plate 203 is switchable between a diffusion state where the incident light is diffused and a non-diffusion state where the incident light is allowed to pass through without being diffused. With this switching of the diffuser plate 203 between the diffusion state and the non-diffusion state, a viewing angle of 2D displaying can be changed. For example, when one user 60 is watching the liquid crystal panel 204, the viewing angle of 2D displaying can be reduced by switching the diffuser plate 203 to the non-diffusion state. Thus, power consumption of the light source 201 required to implement a predetermined display luminance can be reduced. Moreover, since the light from the liquid crystal panel 204 is not spread out, the privacy of displayed data can be protected. On the other hand, when two or more users 60 are watching the liquid crystal panel 204, for example, the viewing angle of 2D displaying can be increased by switching the diffuser plate 203 to the diffusion state.
Next, a configuration of a conventional 3D display is described. FIG. 12 is a diagram showing a configuration of a conventional liquid crystal display device 30 capable of 3D displaying. The liquid crystal display device 30 shown in the diagram includes a pair of light sources 301 and 302, a light guide plate 303, a liquid crystal panel 304, and a control unit 305 (see Patent Literature 2, for example). The light source 301 and the light source 302 of the pair are positioned opposite, respectively, to a side surface 303a and a side surface 303b of the light guide plate 303. A prism unit 303c is provided on the bottom surface of the light guide plate 303. The shape of the prism unit 303c is designed in such a manner that light from the light source 301 is focused on a right eye 61a of the user 60 and that light from the light source 302 is focused on a left eye 61b of the user 60.
The control unit 305 causes the light source 301 and the light source 302 of the pair to illuminate alternately. Here, suppose that the light source 301 illuminates. In this case, as shown by a solid arrow 306 in FIG. 12, after the light emitted from the light source 301 is reflected by the prism unit 303c of the light guide plate 303, the light is emitted from a main surface 303d of the light guide plate 303 and is then focused on the right eye 61a of the user 60. Next, suppose that the light source 302 illuminates. In this case, as shown by a dashed arrow 307 in FIG. 2, after the light emitted from the light source 302 is reflected by the prism unit 303c of the light guide plate 303, the light is emitted from the main surface 303d of the light guide plate 303 and is then focused on the left eye 61b of the user 60. While the light source 301 is illuminating, the control unit 305 causes the liquid crystal panel 304 to display a parallax image for the right eye. While the light source 302 is illuminating, the control unit 305 causes the liquid crystal panel 304 to display a parallax image for the left eye. With the parallax caused by the different images shown to the right eye 61a and the left eye 61b of the user 60, the liquid crystal display device 30 can provide 3D displaying to the user 60.
When an image is displayed at a narrow viewing angle as in the case of the aforementioned 3D display, the light sources 301 and 302 having small divergence angles are used. In general, each of the light beams emitted from the light sources 301 and 302 has a property of diverging to a certain extent. Here, the divergence angle refers to an angle of divergence measured when the light emitted from the corresponding one of the light sources 301 and 302 enters the corresponding one of the side surfaces 303a and 303b of the light guide plate 303. Each of the light sources 301 and 302 having the small divergence angles can be configured with, for example, a light emitting diode (LED) light source and a collimator lens that is positioned between the LED light source and the light guide plate 303. By using these light sources 301 and 302 having the small divergence angles, divergence of the light to be emitted from the liquid crystal panel 304 can be reduced. This can prevent crosstalk from occurring. Here, crosstalk is a phenomenon in which a parallax image that should enter one of the eyes of the user 60 undesirably enters the other eye as well.
It should be noted that, by setting the same parallax image for the right eye and the left eye, the aforementioned liquid crystal display device 30 can function as a privacy display. The privacy display is used for preventing an image displayed on the liquid crystal panel 304 from being peeked by a third person other than the user 60.